1. Field of the Invention
The present invention generally relates to the area of audio enhancement technology in personal computers, and more particularly to a method and system for processing audio signals for the purpose of perceptually improving the quality and characteristics of the audio signal to the satisfaction and enjoyment of listeners.
2. Description of the Related Art
The transfer of digital audio files to terminal devices through the Internet, wired or wireless networks has gained substantially in popularity in recent years. This increase is due in part to the availability of transportable compressed file formats that may be used to regenerate relatively high quality output audio signals from the compressed file formats received or stored at the terminal devices (e.g., multimedia computers and handheld digital audio players).
Digital audio signals typically consist of 16-bit samples recorded at a sampling rate more than twice the actual audio bandwidth (e.g., 44.1 kHz for compact discs). For example, given 16-bit samples at a sampling frequency of 44.1 kHz, without the compressed file formats, one minute of mono audio would require 5.1 Mbytes of memory and one minute of stereo audio would require 10 Mbytes of memory. A typical compact disc containing digital audio information has an approximate storage capacity of 783 Mbytes which would, for example, provide 74 minutes and 33 seconds of stereo music. However, it would take over 30 hours to download an uncompressed album length audio file of this type using a 56 K modem.
Using a standard audio compression methodology such as MPEG Audio Layer 3 (MP3), a CD quality sound file may have the same amount of data but compressed by a factor of 12 for efficient transmission to the terminal devices. The reduction of data reduces the download time considerably over standard network connections (i.e., the Internet), which makes it possible now to transfer digital audio files over a network. But the reduction of data is achieved by minimizing xe2x80x9credundant informationxe2x80x9d in the data. In fact, some data reduction processes have introduced undesirable side effects that degrade the original quality of the sound. Specifically, some of the data reduction encoding methods currently used degrade the bass and high frequency ends of the audio spectrum and add audible artifacts which are particularly noticeable on low quality sound delivery systems such as those low-priced audio systems for a multimedia personal computer.
Additionally, many digital audio files are generated from analog sources that are often monaural and lacking depth in the low and high frequency ends of the audible spectrum due to the particular recording methodology used. These recordings lack the perceptual characters and dynamics of the original audio signal and quite often contain an inordinate amount of audible artifacts.
There is therefore a need for a solution that will enable any digital audio reproduction devices to enhance the low and high frequency ends (i.e., bass and treble) of the output signal resulting from stored digital audio files, to remove audible artifacts resulting from the compression or recording processes and to generate stereo images to enhance monaural digital audio files so that users or listeners can enjoy the processed sound to a great extent.
According to the principles of the present invention, an input signal is passed through three processing modules; a Bass Maximizer module, a Harmonic Exciter module and a Quasi Stereo module. The Bass Exciter module enhances the intensity, depth and punch of the bass audio content by creating harmonic sequences from low frequency components contained in the original input signal. The Harmonic Exciter module adds to the treble audio content of the original input signal by generating harmonic series from the high frequency components contained in the input signal. The Quasi Stereo Module creates a stereo image of the enhanced input signal by adding and subtracting delayed and filtered versions of the enhanced input signal with itself to create left and right channeled stereo-like outputs.
The present invention may be implemented as a method, an apparatus or in a computer readable medium. The advantages of the invention are numerous. Different embodiments or implementations may yield one or more of the following advantages. One advantage of the invention is that it facilitates separate modification and enhancement of the low end frequency components (bass) and the high end frequency components (treble) in digital audio files. Another advantage of the invention is that it facilitates the generation of high quality stereo images from monaural input signals. Still another advantage of the present invention is that it processes audio files in real time with minimal utilization of the processing system""s resources.
Other objects, together with the foregoing are attained in the exercise of the invention in the following description and resulting in the embodiment illustrated in the accompanying drawings.